\usetikzlibrary{shadows}
\usetikzlibrary{arrows}
\begin{tikzpicture}

\node [shape=circle, minimum size=0.5cm, very thick, draw=black] (v0) at (-5,1) {};
\node [ shape=circle, minimum size=0.5cm, very thick, draw=black] (v1) at (1,1) {};
\node [ shape=circle, minimum size=0.5cm, very thick, draw=black] (v2) at (7,1) {};
\draw [-latex, -triangle 45, very thick, bend right, color=blue] (v0) edge (v1);
\draw [-latex, -triangle 45, very thick, bend left, color=blue] (v0) edge (v1);
\draw [-latex, -triangle 45, very thick, color=blue] (v1) edge (v2);
\node at (-5,1) {\Large $s$};
\node at (7,1) {\Large $t$};
\node [color=blue] at (-2,2.4) {\Large $\frac{\sqrt{a}}{n}$};
\node  [color=blue] at (3.8,1.3) {\Large $1 $};
\node  [color=blue] at (-2,-0.4) {\Large $1- \frac{\sqrt{a}}{n}$};

\end{tikzpicture}